These conical intersections are fundamentally different from the ‘H-vinyl’ structures found in simple alkenes because they involve the interaction of four sigma electrons, as opposed to two pi electrons and two sigma electrons.

The sigma bond occupies the internuclear space, and the two pi bonds are at 90° angles to each other surrounding the carbon-carbon internuclear space.

The triple bond is composed of one sigma bond from overlap of sp hybrid orbitals, and two pi bonds, from overlap of two sets of p orbitals.